Liquid-liquid mass transfer in square micro-channels
Multi-scale and/or multi-disciplinary approach to process-product innovation
Innovative Process Equipment-Operation Design & Analysis (T3-10)
Keywords: mass transfer, micro-channel, spectrophotometry
The estimation of a solute transfer between two immiscible liquid fluids is fundamental to predict extraction process or two-phase reactive system behaviour. The empirical correlations that are commonly used to estimate the mass transfer coefficients may not be appropriate in micro-scale since they assume that the interfacial region is composed of a very thin layer in which only diffusion insure the transportation of the solute. The characteristic length of a micro-channel is such that this film thickness is of the same order of magnitude than the channel diameter and convection may strongly contribute to mass transfer in this zone.
This work describes mass transfer experiments done in 100 μm square microchannels. The system is made out of silicium and glass. The micro-channels are engraved in the silicium part by photolithography. Then the two parts are stuck together by anodic bonding. The phases flow according to a slug pattern: droplets are generated in a T-shape junction. Due to the hydrophilic properties of the channel walls, the continuous phase is aqueous while the dispersed phase is organic.
The experiments are performed with water and toluene. The solute to be transferred is acetone. It is initially introduced in the dispersed phase and the concentration of solute is measured in the continuous phase at different times in the channel by UV-spectrophotometry. Therefore, the experimental set-up allows following the enrichment of the aqueous phase in acetone. The continuous phase is partially and permanently extracted from the main channel by secondary channels which are directly connected to the analysis cell.
The mass transfer fluxes are calculated and studied function of operating parameters such as droplets velocities, shapes and frequencies. This study allows suggesting a first approach model on the mass transfer, and distinguishing the contribution of the different surfaces on the interfacial transfer between the two phases (i.e. lateral and caps zones).
Presented Thursday 20, 11:40 to 12:00, in session Innovative Process Equipment-Operation Design & Analysis (T3-10).
